The present invention relates to an information recording and reproducing method and apparatus capable of recording or reproducing FM-modulated analog codes, such as image and voice signals and digital information, for example, data used in computers, facsimile signals and digital audio signals, using a recording beam, such as laser light, in real time.
Recently, a high-density optical recording technique with increased capacity has been developed. However optical recordings have the limitation that a diameter of a recording bit is about 500 nm due to the diffraction of light. The diffractive limitation is directly proportional to the wavelength of light and inversely proportional to a numerical aperture (NA) of a lens. Accordingly, an orientation for high-density recording is to shorten the wavelength of light and increase the numerical aperture of an objective lens. Alternatively, it is possible to utilize the optical phenomenon independent of the diffractive limitation. One method for manufacturing a recording medium involves forming a super-resolution film on a recording film. Further, in an optical head, an attention is paid to a near-field in light recently as a method of pushing forward the above methods. For example, as described in U.S. Pat. No. 5,121,256, a solid immersion lens (SIL) is used to attain a large numerical aperture, so that a smaller spot diameter is obtained as compared with that of a conventional optical lens. The principle thereof is now described. The solid immersion lens is provided by polishing a spherical lens made of transparent material and having a large refractive index n into a hemisphere, for example. Laser light concentrated by an objective lens then becomes focused on the polished surface or flat surface. The velocity of laser light in the solid immersion lens slows by the refractive index and the wavelength thereof is shortened to 1/n. That is, the diffractive limitation in the solid immersion lens reduces to 1/n as compared with a usual value. From a different viewpoint, it may be stated that the numerical aperture (NA) of the objective lens can increase by n times. In this time, the numerical aperture increases within the solid immersion lens, although when the laser light passes through the solid immersion lens into air, the diameter of the beam spot thereof returns to the former diameter again. However, when the distance between the flat surface corresponding to a bottom surface of the solid immersion lens and a sample (such as a recording film of a disk) is shortened to 200 nm or less (near-field), the laser light is transmitted to the sample, while the wavelength thereof stays at 1/n as compared with the wavelength .lambda. of incident light and accordingly the resolution increases with n times. That is, the diffractive limitation reduced to 1/n, as compared with the usual value, can be obtained.